A-300 PRO, problem with values over 121

Hello.
My A-300 PRO mus have some kind of issue with values over 121.
Volume faders and pan knobs reaching beyond 121 start sending values in a neverending loop.
The values sent in this state are all greater than 121.
It only stops when I move the fader or knob under 121 again.
Under 121 it works ok.
Anyone may know something about it?
Thanks.